JVC Procision LT-47X899

Black Level (5.16)
The black level is a critical part of the performance of a TV; the deeper the blacks, the higher the contrast and the better the display will be at keeping the dark bits in scary movies properly dark. We measured the darkest black that the LT47X899 could produce at 0.37 cd/m^{2 (} Candelas per square meter), which is a reasonable level for an LCD screen. Because LCDs use a backlight, the blacks are never going to be as deep as a Plasma screen (where the light is generated by the plasma; if the plasma is not being activated, there is little or no light). But the 0.37 cd/m² of this display means that blacks aren't really all that black; there is still some light getting through the screen, and this is always visible as a pale light on even the darkest screens.

Another interesting thing to note is that the display has an automatic dimming feature; if you display a nearly all-black screen, it automatically turns down the backlight after about 20 seconds. There is no way to disable or control this feature. Peak Brightness (8.84)
At the other end of the spectrum is the peak white; the brightest white that the display can produce. We measured this at 307.44 cd/m², which is a decent, if unspectacular score. This means that the white parts of the screen are going to be pretty bright, and a decent peak brightness also means that the display will hold up better in situations with lots of ambient light (such as watching TV in daylight). Contrast Ratio (5.74)
Contrast is the ratio of the darkest black to the brightest white, and it is the figure that many TV manufacturers use to advertise their models, as a higher contrast ratio means darker blacks and brighter whites. We measured the contrast ratio of the LT-47X899 at 831:1, well below the manufacturer quoted figure of 3500:1. That's because the figure they quote is for what they call dynamic contrast ratio, where the whites are measured with the backlight on full, then the blacks with it turned down to make the blacks darker. Our test measures what's often called the static contrast ratio, where the backlight remains at the same level (maximum) all the time; we feel this is the more important figure, as it represents what you will get when using the display. 890:1 is an acceptable figure for an LCD TV, but it is not overly impressive; several HDTVs have much better scores here. Tunnel Contrast (8.38)
The black level test that we do above is based on how dark an all-black screen is, but that's not a situation that occurs in the real world that often. What you more often get is scenes that contain areas of white and black next to each other, which is why we also test what we call test tunnel contrast. In this test, we look at if the black on the screen stays black when it is surrounded by white, by measuring a small area of black that's surrounded by differing amounts of white. On many displays, some of the white leaks into the black area, making blacks look lighter and lessening the dramatic impact of a scene. The graph below shows our measurements of the small area of black in the center of the screen as more and more white is put around it, until 95% of the screen is white. The ideal for this would be a flat curve on the graph, which would mean that the black remains at the same level, irrespective of how much white surrounds it.

As this graph shows, the blacks stay pretty dark on the LT-47X899 as the amount of white increases; there is only a slight increase in the luminosity of the black area as it is surrounded by more and more white. In fact, the luminosity of the black area only increases by about 0.2 cd/m² when the black area is surrounded by 95 per cent of white on the rest of the screen. This is good, as it indicates that the only a small amount of the light from the white area of the screen is escaping into the black area. So, if you are into film noir, you should have no problem picking out Harry Lime in The Third Man's Vienna street scene on this display.

White Falloff (7.21)
The flip side of the performance of displays is how well it displays larger areas of white. In our peak white test, we measure a small area of white on the screen, but brightness of the white can often change depending on how much white there is on screen. On some displays (particularly plasma displays), the white gets paler as the amount of white on the screen increases, as the display generates more heat when it is displaying an all white screen, so it turns down the luminance to stop it from melting. On others (such as most LCDs) the whites get brighter as the amount of white on the screen increases. So, we test this by displaying a sequence of progressively larger areas of white and measuring the luminosity of the center of the screen. The graph below shows the result of this; the luminance of the white on the screen increases slightly as the amount of white on the screen goes up.

In this test, the luminance of the white started at 280.19 cd/m2 with five percent of the screen white, then increased to 303.7 cd/m2 with all of the screen showing as white. This lack of any major change in brightness is a fairly common behavior we see with LCD displays, and it is one of the things that makes them appealing for use in situations where there is a lot of ambient light (such as in a living room with lots of daylight or an office), they start out bright and stay bright as the amount of white increases. Many plasma displays loose brightness when there is a lot of white on the screen, but LCD screen keep a very uniform brightness with both small and large amounts of white on the screen.

Uniformity (6.75)
Having a deep black and bright white screen isn't going to help if the screen is not uniform; dark spots in white areas or there are bright spots in the dark bits are going to distract from the image on the screen. So, we do extensive testing of the uniformity of the screen, using several test screens in DisplayMate that highlight any issues here. We didn't find many issues with the LT-47X899, but there were a few. We found that, on our review display, the top right corner of the screen was a bit darker on white screens, and the bottom right was a little lighter on dark screens. Both of these issues may be slightly distracting in some situations; if you are watching a dark movie, you might notice the brighter corner, and the difference in the corner on white screens is noticeable if you are using the display as a computer screen. But these are fairly minor issues, and they won't be noticeable in most situations. Grayscale Gamma (7.78)
Update: We have rescaled our scoring for this section. The original score was 8.66.

The Gamma correction of a display relates to the way that the display converts the intensity of the incoming signal into the intensity of the light coming from the screen. In order to correctly represent the level of the signal, the display has to process it using something called Gamma Correction. That's what we test here; the way that the display converts the incoming signal into the light you see coming off the screen. We test this by feeding the TV a series of white screens of slowly increasing intensity, and measuring the luminance of the screen. The graph below shows how the screen luminance increases as the signal intensity increases.

Because of the way that the eye interprets light, we don't get a straight line from this. However, we can analyze the curve a little easier if we plot it on a graph with logarithmic axis, such as the one below. On this graph, the luminance is show by the black line, while the blue line shows the trend line for the main part of the curve. An ideal display would follow this trend line exactly. In reality, most are close, but not always right on.

The LT-47X899 did a reasonable job here; the curve follows the trend for most of its length, only going a bit off track at the bottom end. This indicates that some of the darker shades of gray change suddenly from one level of brightness to another, which could lead to some banding in dark parts of the image. However, this is a minor issue.

We also measure the gamma correction, a number that indicates the shape of the curve in the first graph. There is no perfect figure here; instead, we look for the gamma to be within a range of 2.4 to 2.5, and the LT-47X899 falls just a little outside of this range at 2.57. This is not far enough outside of our ideal range to be a big problem, but it is less than ideal; the gamma is a bit high, which could make some images on the screen look a bit flat as some grays may be slightly darker than they should be. But it's an acceptable figure, and that should not prove to be a big problem.

Resolution Scaling (6.21)
We do most of our tests feeding the display a signal at the highest resolution the display supports (for the LT-47X899, that's a 1080p signal), but that isn't what the display will always have to work with. Many devices (such as DVD players, cable boxes and game consoles) produce a lower resolution signal will also be connected to the display, and the display will have to scale and process these to display them on the screen. So, we test how well the display scales these by feeding it a signal at each of the lower resolutions (in this case, 480p, 720p and 1080i) and examining how well the display deals with scaling these to fit the screen.

One interesting thing to note here is that the LT-47X899 has an aspect ratio button on the remote, which has a big effect on the way it deals with lower resolution signals. Some HDTVs move this control to an on-screen menu or otherwise hide it, but it's right there on this one, on a button the same size as the menu button. This is both a good and a bad thing; it's a good thing if you connect an older analog TV source (such as an old DVD player or a VHS video recorder) as you can change the aspect ratio to make the video fit the screen as required. The modes on offer vary with the input device, but for an analog source, you get the choice of Panorama (which stretches the width of the image to a bit beyond the screen width), Cinema (which stretches both the width and height to go beyond the screen size), Full (which stretches the image to overscan slightly on the screen) and Regular (which fits the image to a standard definition 4:3 aspect ratio). With a digital signal, you get the choice of Panorama Zoom, Cinema Zoom (which behave the same as their analog cousins), Full (which scales the display to overscan slightly on the screen), Full native (which scales it to fit the screen exactly) or the oddly named Slim, which scales the screen down to a 4:3 aspect ratio. Perhaps the latter was designed to help people who are concerned about their weight; if you view a widescreen signal in this mod, everybody looks as thin as a supermodel.

The downside is that these choices are somewhat redundant when you're watching a high definition digital source, and that the LT-47X899 defaults to the Full mode, which means that the image is a little overscanned. This is especially irritating if you are trying to use the display with a computer, as the menu bars at the bottom or edge of the screen aren't visible; to get them, you have to switch the display to the Full Native mode every time you turn the TV on or change inputs.

480p (7.13)
480p signals are produced by devices such as DVD players and older cable boxes that display standard definition TV. We found that the LT-47X899 did a decent, if unspectacular job of displaying this type of signal; the image was extremely soft, which meant that text at smaller font sizes was mostly unreadable. But the flip side of this is that the image didn't have the problems we often see with displays that overly sharpen the image to make it look more like a high definition one; we didn't see much evidence of issues such as moire patterns in screens that use alternating black and white lines, or patterns caused by the sharpening process. The image was overscanned by around 2.5 percent, which means that the edges of the image were slightly trimmed off, but not to an unacceptable degree.

720p (5.38)
Many broadcasters use a 720p signal when they are broadcasting sports, as the progressive nature of the signal (where it contains 60 full frames per second, instead of the interlaced frames of 1080i) makes for smoother movement on the screen.  And the LT-47X899 did a moderate job of displaying this mode; we found that text was only legible at medium and large font sizes, and that the image was still somewhat soft. Unusually, the LT-47X899 had some overscan here (about 2.5 percent, the same as the 720p signal); most TVs don't overscan a 720p signal.  Although the LT-47X899 has several aspect ratio modes available from the remote, none of them got rid of this overscan, as the Full Native mode was not available when displaying a 720p signal. But the overscan wasn't a big problem; it just means the edge of the screen is slightly trimmed off, which would only be an issue if you were using the LT-47X899 as a PC monitor in 720p mode. And as most graphics cards can now produce a 1080p signal, this shouldn't be a big issue for most users.

1080i (6.23)
1080i is the format that most people associate with high definition TV; it's what most high def cable boxes and satellite boxes produce. And the LT-47X899 did a reasonable job with this type of signal; text was moderately sharp (all but the smallest fonts were visible), but there was some evidence of moire patterns in our test screens; these screens use a series of patterns of gray and black dots to see how the screen processes the image, and these had an odd, almost checkerboard-like look to them. As we noted above, the LT-47X899 defaults to the Full aspect mode, but switching this to the more appropriate Full Native mode didn't make things any better. In this, some of the screens had a greenish cast.